The goal of this research is to designate the retinal circuits involved in the processing photic, and especially chromatic, information among the vertebrates. The circuits are to be specified in terms of (1) neuronal morphology, (2) spectral response properties, (3) connections with other neurons and (4) neurotransmitters involved. Central to the investigation is the concept that microchemical methods are useful probes of the light responses of populations of neurons; that light-induced variations in neuronal chemical behaviors (such as neurotransmitter uptake or sugar and nucleotide incorporation) can be measured with light and electron microscope autoradiography. The project has already achieved the identification of five (possibly six) distinct classes of retinal interneurons that use various neurotransmitters and has permitted specification of the light responses of entire populations of these neurons based upon variations in neurotransmitter uptake. Specifically: type H1 horizontal cells are GABA-ergic and hyperpolarize to all wavelengths, especially red lights; type Ab amacrine cells are GABA-ergic and red-depolarizing; a possible second kind of GABA-ergic amacrine cell isbeins studied; type Aa amacrine cells are glycinergic and red-hyperpolarizing; two types of interplexiform cells have been found, one glycinergic and the other dopaminergic. Ultrastructural studies of connections of GABA-ergic neurons are largely complete; studies of glycinergic and dopaminergic neurons are in progress.